On the first sample you can create a brush in photoshop that gives you that finish; In Photoshop CS4 which is the one I have now I found brush 59px or 39px that could give you that effect.
You can also draw directly in a piece of acetate with a sponge and create the effect to then burn it in a silkscreen and come up with a result like it.
The second one could also be a big brush in photoshop, but I could also think that if you
don't ink a silkscreen evenly you would have this result.

Hope this helps.

Patty

Good lord.

I used to work my butt off trying to avoid effects like that :o)

silk screen is a visceral medium. You can create the exact effect you like digitally, or you can play around and you could come up with something magical, be it as simple as a dull and nicked squeegee, rough texture under your paper or some judiciously placed dirt on the screen...

Hi Daniel,
First one looks as designed that way.
The second looks like silkscreen made without the paint (clearance after work). Or it is a scan of faxed picture, or bad laserprinter printout. I vote for the latest.
BTW silkscreen could be very accurate. Macrophoto of business card I made many yers ago (for Ammirati, Puris, Lintas):

seconding JanekZ; yes, screen printing can be very accurate. I used to screen print tiny, tiny little circuit boards using a stainless steel mesh, and -not sure what to call them, but sort of like pegs on circuit display boards in hydro generating plants that had less than a thousandth of an inch tolerance. The registration was set with a micrometer and a magnifying glass.